1. Field of the Invention
This application relates to new propulsion systems for submarine vessels and submarine vessels comprising such systems. More particularly, it concerns a new form of shaftless thrusters for submarine propulsion and submarine vessels equipped with such thrusters.
2. Description of the Prior Art
Submarine searches, research, investigations and like operations are accomplished with the use of special design submarine vessels. Typically such vessels are of two different types, i.e., personnel operated submarines and remotely operated vehicles (ROVs). Regardless of the type, there is a continuing need to reduce their power consumption and maintenance requirements while increasing their efficiency of operation. The present invention provides improved propulsion systems that help meet these demands.
Most modern underwater propulsion systems or thrusters, house a conventional electric motor in a pressure proof housing with gear reductions and special high pressure shaft seals, or no gear reduction, special seals and special high speed propellers. Both types utilize nozzles around the propellers to improve efficiency by reducing blade tip vortex for converting the centrifugal component of propeller induced water flow to axial thrust.
A naked, shaft driven propeller wastes a considerable amount of power, especially at low forward speed, through centrifugal eddy currents around the tips of the blades. The well known Kort nozzle limits the waste by limiting the eddy currents at the tips.
A "ring propeller" is one in which the nozzle is permanently attached to the propeller blade tips, and turns with it. At slow speeds, thrust is improved for a given power input. In contrast, the nozzle may remain fixed relative to its vessel while the propeller rotates within it to benefit from the nozzle's liquid flow control while propelling the vessel.
The most efficient portion of a propeller is the outer area of the blades. The hub of a central shaft driven propeller does little except hold the blades in position and transmit the torque to rotate them. Since the blades do the work, the hub and shaft must be substantial to provide the torque which the blades then translate into thrust. These factors concerning marine propellers are well known so a type of propeller has been designed that eliminates a central drive shaft as disclosed in U.S. Pat. No. 3,487,805. The present invention provides further improvements in this type of marine propeller.
Another serious reason for elimination of drive shafts and all other thru-hull shafts in manned and unmanned submersibles is to improve the integrity of the hull and motor housings. Thus, particularly with the motor housings, flooding occurs with undesired frequency due to the presence of thru-hull shafts and the stress imposed on thru-hull seals. Pressure in deep water submersibles increases with depth at about 1/2 psi per foot of depth. Thus, a submersible designed for operation at depths of 3000 ft must have seals on a thru-hull shaft capable of withstanding external pressures of about 1500 psi. The present invention addresses this hull integrity problem in the use of deep water submersibles and eliminates it by provision of new thrusters that require no thru-hull shafts and seals.